Glendale students in grades seven through 12 now have 30 days from the first day of school on Aug. 29 to be re-immunized for pertussis, or whooping cough. The extension was invoked after district officials said that with just two weeks before the start of school, roughly one-third of students have yet to show proof of immunization.

“There are many people on vacation while this is going on, I think it would be good for flexibility,” school board member Greg Krikorian said.

Originally, students were told they must comply by the start of the academic year, but Gov. Jerry Brown last month signed legislation allowing districts to loosen the deadline after school officials said they might be forced to turn away students at the door.

“The students will be enrolled conditionally, and the school would follow up to make sure the student had the vaccine in 30 calendar days and that would be Sept. 27,” Assistant Supt. Katherine Fundukian Thorossian said of the terms of the waiver.

The immunization is being administered as part of a three-in-one shot known as Tdap, which protects against diphtheria, tetanus and pertussis. It was added to the list of required vaccines after an outbreak of whooping cough killed 10 infants in California last year.

District officials launched a public information campaign in spring to inform parents of the new requirement, posting information on their websites and sending home fliers in student folders. They also hosted low-cost and free inoculation events, and placed automated and personal telephone calls to families still needing to show proof of the vaccine.

But with the first day of school less than two weeks away, roughly one third of those students who must show proof of vaccination have yet to do so, officials said. At Hoover High School alone, roughly 800 students still need to confirm they received the Tdap shot, said Principal Jennifer Earl.

The district will offer two additional on-the-spot vaccination opportunities: Aug. 23 at Glendale High School and Aug. 24 at Hoover High School. The events will run from 8 a.m. to noon, and parents must accompany their children to sign the appropriate paperwork, Thorossian said.

The Tdap shot will cost $40, and cash is required, she added.

Despite the extensive publicity, there will be families who need that extra 30 days to comply with the vaccine requirement, school board member Mary Boger said.

“They may be coming from another state, or another county where it hasn’t been as well publicized,” Boger said. “We will have students and parents who show up on the first day of school saying they didn’t know they had to do it, so I absolutely support the waiver.”